Internal combustion engine emissions regulations have become more stringent over time. Also, the demand for high fuel economy has increased greatly to conserve fuel and reduce green house gas emissions. Advanced combustion systems using premixed compression ignition offer the combined benefit of low temperature combustion to simultaneously reduce oxides of nitrogen (NOx) emissions and particulate emissions with high fuel economy. Examples of these systems include homogeneous charge compression ignition (HCCI), premixed low-temperature diesel combustion (PLTDC), and gasoline direct injection compression ignition (GDCI) see Kobayashi et al., “Internal Combustion Engine,” US Patent Application US2008/0275621 A1. All of these systems require sufficient mixing of the fuel and air prior to compression ignition and heat release.
Variations in the combustion process may affect engine emission levels and/or fuel economy. Causes of such variation may in general be classified as either external causes such as changes in ambient temperature, pressure and humidity, and fuel properties or formulation; or internal causes such as engine aging, part to part variation within an engine, and engine to engine variation during manufacturing. These variations may change the state of fuel-air mixing or change the ignition delay period. This may lead to non-optimized combustion, especially when open-loop (OL) control is used. Various closed-loop (CL) combustion control strategies have been proposed. Some strategies use in-cylinder pressure sensors or in-cylinder ionization sensors to indicate combustion phase information by measuring a condition present in the combustion chamber indicative of when combustion of an air/fuel charge begins, ends, or is completed by a percentage. In general, CL combustion control can better compensate for variations in combustion due to the external and internal causes described above.
CL combustion control strategies using in-cylinder pressure sensors or in-cylinder ionization current sensors to provide one or more of several available control metrics have been proposed. For example, CL combustion control strategies using in-cylinder pressure sensors to determine a closed-loop control metric have been proposed that: a) determine a crank angle location when 50% of the fuel in the combustion chamber is burned (CA50), see Haskara et al., “Internal Combustion Engine Exhaust Gas Recirculation Control,” U.S. Pat. No. 7,231,905; b) determine a crank angle location when a maximum combustion chamber pressure occurs, see Müller et al., “Combustion Pressure Based Engine Management System,” Society of Automotive Engineers (SAE) 2000-01-0928; c) determine a maximum net pressure acceleration point, see Zhu et al., “MBT Timing Detection and its Closed-Loop Control Using In-Cylinder Pressure Signal,” SAE 2003-01-3266; and d) use a combustion chamber pressure-ratio management (PRM) strategy, see Matekunas, “Engine Combustion Control with Ignition Timing by Pressure Ratio Management,” U.S. Pat. No. 4,622,939 and Sellnau et al., “Cylinder-Pressure-Based Engine Control Using Pressure-Ratio-Management and Low-Cost Non-Intrusive Cylinder Pressure Sensors,” SAE 2000-01-0932. For CL combustion control using ion sensors, several control metrics have been proposed such as: e) determining an end of ignition phase for spark-ignited gasoline engine, see Latsch, “Method and Apparatus for Closed-Loop Ignition Time Control,” U.S. Pat. No. 4,377,140; and f) determining a start of combustion, see Huang et al., “Investigation of an In-cylinder Ion Sensing Assisted HCCI Control Strategy,” SAE 2005-01-0068 and Raichle et al., “Method and Device for Evaluating an Ion Current Sensor Signal in an Internal Combustion Engine,” U.S. Pat. No. 6,614,230. However, many CL combustion control strategies using in-cylinder pressure and ionization current sensors rely on control metrics that lead to complicated real-time algorithms that are difficult to calibrate. Advanced combustion systems may also require new control strategies to achieve both low emissions and high fuel economy. The choice of control metric for CL control is very important in order to deliver robust combustion control in an IC engine with less computational efforts and costs.